{"id":2302,"date":"2020-09-01T14:13:05","date_gmt":"2020-09-01T13:13:05","guid":{"rendered":"http:\/\/www.btaloos.co.uk\/?p=2302"},"modified":"2020-09-01T14:13:05","modified_gmt":"2020-09-01T13:13:05","slug":"coronavirus-sars-cov-2-covid-19-and-hvac-systems","status":"publish","type":"post","link":"http:\/\/www.btaloos.co.uk\/?p=2302","title":{"rendered":"CORONAVIRUS, SARS-COV-2, COVID-19 AND HVAC SYSTEMS"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

This response outlines the current understanding of the possible routes of transmission of the SARS-CoV-2 virus (including airborne aerosol transmission) and possible responses that Building Services Engineers can adopt to reduce transmission risks in the built environment.<\/strong><\/p>\n\n\n\n

The current coronavirus (COVID-19) outbreak continues to develop rapidly\nwith relevant advice being updated regularly and an increasing body of research\nbeing published.\u202f <\/p>\n\n\n\n

Government<\/a>, NHS<\/a> and Public Health England<\/a> websites, as well as those of\nthe devolved administrations should be consulted for current policy across the\nUK.\u202f <\/p>\n\n\n\n

CIBSE is the UK member of REHVA, the European Federation of Heating and\nVentilation Engineers. REHVA has developed a COVID-19 guidance webpage<\/a> giving information and guidance<\/a> and has developed a bibliography<\/a> on how to operate and use building services to minimise the spread\nof the virus through HVAC or plumbing systems. The guidance was further updated\non 3rd<\/sup> April 2020 to reflect new knowledge and evidence becoming\navailable. <\/p>\n\n\n\n

Current Public Health England guidance on infection control<\/a> states that\n\u201cThe transmission of COVID-19 is thought to occur mainly through respiratory\ndroplets generated by coughing and sneezing, and through contact with\ncontaminated surfaces. The predominant modes of transmission are assumed to be\ndroplet and contact.\u201d (See section 2.1 of the guide).  <\/p>\n\n\n\n

Droplets will generally fall out of the airstream within a short\ndistance (depending on airflow speed and direction), hence the guidance to\nremain 2m apart. However, these may evaporate, reducing in size and mass and\ntravel further in air streams, contaminating surfaces and increasing the risk\nof airborne transmission.<\/p>\n\n\n\n

While airborne transmission is not thought to be a primary route of\ntransmission, there is an emerging and growing body of evidence that the\nSARS-CoV-2 can also be spread through the air, particularly in poorly\nventilated indoor spaces, and that ventilation provision in buildings should be\nreviewed in the light of this.\u202fFor an explanation of airborne transmission, see\nthe series of tweets by Prof. Lynsey Marr<\/a>.<\/p>\n\n\n\n

Emerging Findings <\/p>\n\n\n\n

Proving modes of transmission during an outbreak is difficult. However,\nmultiple recent studies are showing evidence of indirect contact (which may be\nlinked to airborne spread) and have also linked airflow patterns to infection cases.<\/a><\/p>\n\n\n\n

This has been particularly the case in high occupancy areas, in spaces\nwith little outdoor air, and when people generate a lot of aerosols (e.g.\nshouting and singing). Given the growing body of evidence suggesting airborne\ntransmission may be a route of infection and knowledge of aerosol generation\nand transport it is prudent to ensure ventilation is operating appropriately to\nprotect occupants.<\/p>\n\n\n\n

The following measures, using outside air wherever possible, should help\nto reduce the risks from airborne transmission. <\/p>\n\n\n\n

Prevention <\/p>\n\n\n\n

The primary mechanisms for preventing the transmission of coronavirus\nremain regular, thorough handwashing using soap and hot water for at least 20\nseconds, coupled with strict adherence to social distancing requirements and\nstaying at home. Surfaces which may be contaminated also need regular cleaning\nfollowing the protocols set out by PHE. <\/p>\n\n\n\n

Dilution of internal air should reduce any risk of potential airborne\nviral transmission by reducing exposure time to any airborne viral aerosols,\nand also reduce the chance for these aerosols to settle on surfaces. Evidence\nshows that virus can survive on some surfaces for at least 72\nhours<\/a> and hence any action to limit surface contamination is beneficial.<\/p>\n\n\n\n

It is recommended that any ventilation or air conditioning system that\nnormally runs with a recirculation mode should now be set up to run on full\noutside air where this is possible. <\/p>\n\n\n\n

In buildings with mechanical ventilation systems extended operation\ntimes are recommended. In demand control systems CO2<\/sub> set points\nshould be set to 400ppm to increase the delivery of outside air. Ventilation\nshould be kept on for longer, with lower ventilation rates when people are\nabsent. It is not recommended to switch ventilation systems off in any\nbuildings, even those temporarily vacated, but to operate them continuously at\nreduced speeds.<\/p>\n\n\n\n

Recirculation of air between spaces, rooms or zones occupied by\ndifferent people should be avoided. However, in the case of any systems\nserving a single space, partial recirculation of air within that space, such as\nthrough a local fan coil unit, is less of a concern. The reason is that the\nprimary objective is to maximise the air exchange rate with outside air and to\nminimize the risk of any pockets of stagnant air.<\/p>\n\n\n\n

If a local recirculation unit enhances air disturbance and hence helps\nreduce the risk of stagnant air then this should be considered when developing\na strategy. Note that although these are relatively uncommon today, ceiling\nfans within a space can provide this function. <\/p>\n\n\n\n

On colder days consideration must be given to human behavioural\nresponses. A ventilation system on full outside air which is not adequately\nheated may create discomfort draughts. This may lead to users seeking to turn\nthe system off, or with naturally ventilated spaces users may close vents or\nwindows. These actions will reduce the air exchange rate and dilution of any\ncontaminants (and not just any viral contamination) and overcome the primary\nobjective of the ventilation strategy. It is important that where users can\nintervene in the control of the ventilation that they are made aware of the\nbenefit of these for reducing the circulation of infectious material.<\/p>\n\n\n\n

Care should be taken with any ventilation grills that can be blocked,\ne.g. floor grilles for displacement ventilation, and occupants educated on the\npurpose and benefits of these. <\/p>\n\n\n\n

The potential benefit to public health at this time outweighs the\nreduction in energy efficiency caused by not recirculating air. Airborne\ncontaminants may be minimised by proper and effective filtration and regular\nmaintenance. Viral material that settles in ductwork will become unviable over\ntime. In the event that some viral material entered ventilation and\nair-conditioning systems prior to buildings being vacated due to the current\nrestrictions, it is extremely unlikely that that material will pose any risk\nwhen those buildings are re-occupied.<\/p>\n\n\n\n

Where cleaning or planned maintenance of ventilation systems is\nrequired, such as in catering premises, it should be undertaken in line with\nagreed industry guidance, including that relating to site operations under\nsocial distancing requirements. Appropriate PPE should be worn and all\nmaterials, including old filters, should be carefully bagged and disposed of\nsafely. Given the requirement for many business premises to close for the\nimmediate future, there is unlikely to be a requirement to undertake work on\ntheir ventilation or air conditioning systems at this time.<\/p>\n\n\n\n

In poorly ventilated spaces with a high occupancy and where it is\ndifficult to increase ventilation rates it may be appropriate to consider using\nair cleaning and disinfection devices. The most appropriate devices are likely\nto be local HEPA filtration units or those that use germicidal UV (GUV)\nradiation. GUV devices use radiation in the UV-C spectrum and have been shown\nto inactivate coronaviruses, although there is not yet specific evidence of the\nefficacy of UV-C irradiation for SARS-CoV-2.<\/p>\n\n\n\n

There are currently uncertainties about a variety of factors affecting\nUV performance including dosage, wavelength and exposure time. In addition,\nconsideration will need to address the specific room and system configuration,\nair flow, distribution and humidity.<\/p>\n\n\n\n

Any potential equipment will need to be properly tested, validated and\nquality assured and demonstrated to provide the specific irradiation properties\nit is designed to and nothing else. It is essential that appropriate safety\ninterlocks are installed to ensure UV cleaning equipment is not operated when\npeople may be exposed to the radiation.<\/p>\n\n\n\n

They can be applied as an upper-room system or a stand alone consumer\nunit, but it is important that these are sized correctly for the room as many\ndo not have the flow rate to be effective in larger spaces. In-duct UV-C is not\nrecommended to control disease transmission unless it is to decontaminate air\nthat is recirculated. Devices that emit ozone or other potentially hazardous\nby-products should not be used in occupied spaces.  Further guidance on\nair cleaning and disinfection is given in CIBSE guide A.<\/a><\/p>\n\n\n\n

Further Guidance <\/p>\n\n\n\n

CIBSE TM40 Health\nand Wellbeing in Building Services<\/a> provides guidance on best\npractice design and operation of buildings to support health, comfort and\ncognitive performance. Key aspects covered include air and water quality and\nthe environment around us: light, acoustics, thermal and humidity conditions,\nand electromagnetic fields. The health and comfort impact of each of these\nenvironmental factors is summarised to provide a background for informed\ndecisions.<\/p>\n\n\n\n

The April 2020 issue of CIBSE Journal carries news<\/a> and opinion<\/a> on COVID 19, and there is a CIBSE Journal podcast<\/a> which addresses the issues in\nfurther detail. <\/p>\n\n\n\n

The REHVA COVID-19 guidance webpage<\/a> provides further information\nand guidance<\/a> and a bibliography<\/a> on how to operate and use building services to minimise the spread\nof the virus through HVAC or plumbing systems.<\/p>\n\n\n\n

References<\/p>\n\n\n\n

The following references inform the emerging view that aerosol\ntransmission of SARS-CoV-2, whether through direct respiratory droplet transfer\nor fomite generation, may in fact be a more important exposure transmission\npathway than previously considered. Many are still undergoing peer-review, but\nthey demonstrate the current thinking based on emerging findings.<\/p>\n\n\n\n

Fears et al, Comparative dynamic aerosol efficiencies of three emergent\ncoronaviruses and the unusual persistence of SARS-CoV-2 in aerosol\nsuspensions https:\/\/www.medrxiv.org\/content\/10.1101\/2020.04.13.20063784v1.full.pdf<\/a>
\nhttps:\/\/doi.org\/10.1101\/2020.04.13.20063784<\/a>
\nPREPRINT posted 18th April 2020 
\n 
\nvan Doremalen, N et al Aerosol and Surface Stability of SARS-CoV-2 as Compared\nwith SARS-CoV-1.  New England Journal of Medicine 2020 doi\n10.1056\/NEJMc2004973 https:\/\/www.nejm.org\/doi\/full\/10.1056\/NEJMc2004973<\/a> 
\nThis letter was published on March 17, 2020, at NEJM.org.
\n 
\nFineberg: Rapid Expert Consultation on the Possibility of Bioaerosol Spread of\nSARS-CoV-2 for the COVID-19 Pandemic (April 1, 2020) (2020) https:\/\/www.nap.edu\/read\/25769\/chapter\/1<\/a> 
\nLetter in response to the consultation.
\n 
\nLidia Morawska, Junji Cao, Airborne transmission of SARS-CoV-2: The world\nshould face the reality, Environment International, Volume\n139,2020,105730, 
\nhttps:\/\/doi.org\/10.1016\/j.envint.2020.105730<\/a>. 
\nThis is a preprint of a paper for publication in the June issue<\/p>\n\n\n\n

Yuguo Li et al : Evidence for probable aerosol transmission of\nSARS-CoV-2 in a poorly ventilated restaurant https:\/\/www.medrxiv.org\/content\/10.1101\/2020.04.16.20067728v1.full.pdf<\/a> Preprint\nposted 22 April 2020<\/p>\n\n\n\n

The Chartered Institution of
Building Services Engineers \u00a0(CIBSE)
Registered as a Charity in England No. 278104<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

This response outlines the current understanding of the possible routes of transmission of the SARS-CoV-2 virus (including airborne aerosol transmission) and possible responses that Building Services Engineers can adopt to reduce transmission risks in the built environment. The current coronavirus (COVID-19) outbreak continues to develop rapidly with relevant advice being updated regularly and an increasing<\/p>\n","protected":false},"author":3,"featured_media":2304,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2302"}],"collection":[{"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2302"}],"version-history":[{"count":2,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2302\/revisions"}],"predecessor-version":[{"id":2306,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/2302\/revisions\/2306"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=\/wp\/v2\/media\/2304"}],"wp:attachment":[{"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2302"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2302"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.btaloos.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2302"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}